1. Field of the Invention
The present invention generally relates to the field of electromagnetic wave sensor assemblies, and more particularly, to a conversion structure, an image sensor assembly and a method of fabrication a conversion structure.
2. Description of the Prior Art
With the advent of the aging society, the focus on the development of methods for preventive medicare has attracted much attention, especially to the development of equipments for medical diagnostic imaging due to its high technical threshold, high value-added benefit and non-invasive properties. Generally, the types of the medical diagnostic imaging equipments include X-rays systems, electrocardiography (ECG) systems, ultrasonic diagnostic systems, computed tomography (CT) systems, magnetic resonance imaging (MRI) systems, and so forth. Among these types of equipments, X-ray and computed tomography systems are widely used in various medical fields, such as dentistry, orthopedics, chest medicine x-ray radiography and so on.
Generally, the diagnostic X-ray systems and the computed tomography systems are equipped with an X-rays image sensor assembly so as to convert the X-ray beams penetrating through a human body into corresponding electric signals. The electric signals are then transmitted into circuits and calculated by a processor respectively. In a conventional X-rays image sensor assembly, a conversion structure and a light sensor assembly are incorporated as parts of the X-rays image sensor assembly. The conversion structure can convert X-rays into electromagnetic waves which are detectable by the light sensor assembly. The light sensor assembly can further convert the electromagnetic waves into the corresponding electric signals. The conversion structure described above generally uses a scintillator as a material for converting X-rays into the electromagnetic waves and the composition of the scintillator is usually cesium iodide doped with thallium (CsI:Tl).
However, there are many drawbacks when using scintillators as main active components in the X-rays image sensor assemblies. For example, in order to prevent toxic heavy metals, i.e. Tl, from causing environmental pollution and from negatively affecting human health, expensive waste gas filtration systems are required for the process of manufacturing the scintillator. In addition, in order to prevent light scattering when the light passes through the scintillator and to improve the resolution of the image sensor assembly, an epitaxial growth process is required, so as to provide an anti-scatter CsI:Tl pillar structure. Furthermore, Tl and CsI can not be mixed uniformly due to their inherent material properties. That is to say, Tl is unevenly distributed within CsI:Tl and causes bad light conversion efficiency. Besides, since CsI:Tl is prone to deliquescence, the sealing degree of the corresponding image sensor assembly needs to be well controlled.
Therefore, there is a need to provide a conversion structure, an image sensor assembly and a method of fabrication a conversion structure that can overcome the above-mentioned drawbacks.